Generators for producing electricity are well known and have been commercially available for many years. These devices typically include an internal combustion engine. They are adapted to provide alternating current (AC) electricity, through a standard two-prong or three-prong plug receiver, at 120 or 240 volts, and at 50 to 60 Hz; also common is an additional 12 volt DC power port for charging lead acid batteries. Devices which use either gasoline-only or heavy fuels only, such as JP-8, diesel fuel, jet fuel or kerosene, are available.
Gasoline has a low-flashpoint (less than −20° C.) and high autoignition temperature (greater than 200° C.). In operation gasoline requires the proper air to fuel ratio and a spark to induce and maintain ignition. A throttle and/or fuel injector is used to meter the fuel/air mixture which is sucked into the cylinders of the engine during operation. The low flashpoint and volatility of gasoline allows starting of the spark ignition engine at temperatures below freezing, allowing for operation over a broad range of temperatures typically between −20° C. to 55° C. In order to obtain acceptable efficiency, a compression ratio of 8:1 to 12:1 is desirable for a gasoline-only engine, which is low enough to allow for manual pull-starting of the engine and the construction of simple lightweight portable engine devices made of aluminum.
Portable gasoline generators have a simple design in order to keep them light, low cost and durable. Such devices include an engine having a carburetor for mixing air and fuel, and do not include a fuel injector. A carburetor jet controls the maximum amount of fuel present in the air-fuel mixture exiting the carburetor, and a choke is used to reduce the amount of air in the air-fuel mixture, for starting the engine. The size of the jet is selected to provide good performance at maximum power of the engine under typical conditions, such as 25° C. ambient temperature and sea level altitude. As the environment of the engine deviates from those typical conditions, the performance of the engine becomes changes. If the environment deviates too much, it is not possible to properly operate the engine unless a different jet is used to increase the air-fuel ratio. For example, at altitudes above 5000 feet, most small portable gasoline generators will not operate unless a different jet is installed into the device. More sophisticated engines, such as those found in modern automobiles, use oxygen sensors and a fuel injector to increase the air in the air-fuel mixture so that the engine will operate efficiently at high altitudes and at higher than normal ambient temperatures. Therefore, in order to use a small portable generator that can be used in a variety of conditions, such as varying altitudes, it is necessary to also have available appropriate tools for opening the generator and removing the existing jet, a selection of jets varying in size, appropriate charts for selecting the correct jet for each altitude, as well as maps or an altimeter for determine the altitude where the generator will be operating. Furthermore, changing out the jet in a small portable gasoline generator is a somewhat complex operation involving opening the engine and handling parts which have been exposed to gasoline, which may not be desirable for typical consumers, especially in the locations where the generator will be used.